Irradiated rare‐earth‐doped powellite single crystal probed by confocal Raman mapping and transmission electron microscopy

The irradiation‐induced damages and structure modifications of rare earths doped powellite single crystal have been precisely studied using optical and electron microscopy techniques, including optical interferometry, confocal micro‐Raman spectroscopy and transmission electron microscopy. The surface of powellite crystal pops out anisotropically after exposing under Ar ion beam, with a saturation swelling value of 2.0% along a‐axis and 1.3% along the c‐axis of powellite at high dose. Raman mapping on focused ion‐beam sections (5 × 3 µm²) perpendicular to the irradiated surface reveals that irradiation damage induces orientation‐dependent compressive stresses in powellite. However, no significant anisotropic effect has been found on the irradiation‐induced structural disorder in powellite. At low dose (0.012 dpa), the main irradiation‐induced defects created in powellite crystal are small defect clusters. By comparison, the dominant kinds of defects in high‐dose (5.0 dpa) sample are dislocations loops and networks. Copyright © 2014 John Wiley & Sons, Ltd.     

Structure and orbital ordering of ultrathin LaVO3 probed by atomic resolution electron microscopy and Raman spectroscopy

Orbital ordering has been less investigated in epitaxial thin films, due to the difficulty to evidence directly the occurrence of this phenomenon in thin film samples. Atomic resolution electron microscopy enabled us to observe the structural details of the ultrathin LaVO₃ films. The transition to orbital ordering of epitaxial layers as thin as ≈4 nm was probed by temperature‐dependent Raman scattering spectroscopy of multilayer samples. From the occurrence and temperature dependence of the 700 cm^–1 Raman active mode it can be inferred that the structural phase transition associated with orbital ordering takes place in ultrathin LaVO₃ films at about 130 K.     

Irradiation effects in CaF2 probed by Raman scattering

The formation conditions and dynamics of Ca colloids and point defects that appear in irradiated single crystals of CaF₂ were investigated by Raman spectroscopy. The intensity changes in the Raman spectra because of the presence of different concentrations of point defects and Ca colloids that emerged in CaF₂ after irradiation with 2.2 GeV Au ions were used to study their distribution and stability under illumination with three laser wavelengths (473, 532 and 633 nm) at different output powers (2 to 200 mW). A damage saturation at a fluence of 6 × 10¹¹ ion cm⁻² was observed. The dependence of the spectral changes on the ion fluence can be described by a core/halo damage cross‐section model. A radius of 13–18 nm was obtained for the outer (halo) cylinder, in agreement with previous swelling studies. Illuminations of irradiated samples with blue (473 nm) and green (532 nm) lasers were found to be extremely efficient in bleaching the samples, while illumination with a red (633 nm) laser did not lead to a sample recovery. This indicates that the bleaching process is governed by recombination of point defects that have to overcome an energy barrier. Typical time constants for the processes involved are presented. Copyright © 2016 John Wiley & Sons, Ltd.     

Silver-island films probed by hyper-Rayleigh scattering and atomic force microscopy

Incoherent second-harmonic generation, or hyper-Rayleigh scattering (HRS), and atomic force microscopy (AFM) are proposed as a combined probe of nonlinear optical and structural properties of silver-island films. HRS and linear (Rayleigh) scattering indicatrices are measured. The correlation function, deduced from the HRS indicatrices and characterising spatial fluctuations of the total polarisation at second-harmonic frequency, has a length scale significantly larger than that of the correlation functions that are obtained from the AFM data and characterise spatial fluctuations of quadratic optical susceptibilities of the dipole and quadrupole types. This difference is interpreted as indicating that the HRS indicatrix shape is determined by the long-range fluctuations of the local-field factors. Received: 16 October 2001 / Revised version: 16 April 2002 / Published online: 6 June 2002     

Raman scattering study of glass crystallization kinetics

Laser induced glass-crystalline transition is studied by light scattering. Three significant effects are observed depending on the incident laser energy density: (i) Spectral band narrowing indicating cluster enlargement constitutes a precursor effect, (ii) an intensity increase effect indicates a rapid rise of the density of clusters attaining microcrystalline size and (iii) a dynamical reversal effect indicative of glass-crystalline instability. Cluster volume and crystallization appear as separate but related threshold phenomena.     

Raman light scattering and electron microscopy of nanocomposites with the metal core-carbon shell structure

The structural state of carbon in nanocomposites that are based on metals (Fe, Ni, Co, and Ag) encapsulated in carbon and produced by the gas-phase synthesis has been investigated using Raman spectroscopy and high-resolution transmission electron microscopy. The average diameter of particles of the initial nanocomposites after the gas-phase synthesis, including the carbon shell, is less than 15 nm and can vary as a function of the conditions and regimes used for their preparation. The shell of the initial nanocomposites, irrespectively of the metal core type, consists of carbon fragments in the form of curved layers with sizes of less than 10 nm in the lateral direction. In the initial nanocomposites, there is no periodicity in the packing of carbon layers in the radial and lateral directions. The structure of the coating is assumed to be similar to the glassy carbon structure characterized by a curvature of carbon layers in different directions, which requires that, in addition to conventional hexagonal cells, the layers should contain pentagonal and heptagonal cells. Heat treatment of the initial nanocomposites Fe@C and Ni@C in butane (700°C, 60 min) not only significantly increases the thickness of the carbon coating but also increases the degree of ordering of curved carbon fragments in the lateral and radial directions. In the composites with Fe, Ni, and Co, along with this form of carbon, semiconducting nanotubes with a diameter of 1.3–1.5 nm are also formed. The composites with silver nanoparticles exhibit the effect of time-fluctuating giant enhancement of the Raman scattering intensity.     

Raman scattering by electron and phonon excitations in FeSi

The temperature evolution of Raman scattering by electron and phonon excitations in FeSi is studied within the range of 10–500 K. At low temperatures, the frequency dependence for the spectra of light scattered by electrons exhibits vanishing intensity in the range up to 500–600 cm^–1, which suggests the existence of an energy gap of about 70 meV. The calculations of the electronic excitation spectra based on the band structure determined using the LDA+DMFT technique (local electron density + dynamic mean field approximation) are in good agreement with the low-temperature experimental data and confirm that FeSi is a material with intermediate electron correlations. The changes in the shape of the electronic excitation spectrum and in the self-energy of optical phonons indicate a transition to the metallic state above 100 K. The analysis of experimental data demonstrates an appreciable decrease in the electron lifetime with the growth of temperature determining the (insulator–poor metal) transition.     

石墨烯的透射电子显微学研究

石墨烯(Graphene)是近几年迅速发展起来的研究热点材料之一,利用透射电子显微镜(TEM)研究Gra-phene的结构特征和原子动态过程,是Graphene研究的重要进展,文章评述了利用透射电子衍射方法对Graphene的层数、堆垛方式、取向和表面形貌等结构特征进行的研究工作,介绍了利用高分辨透射电子显微术在Graphene的表面缺陷、边缘结构及吸附原子等研究领域取得的最新结果.     

石墨烯的透射电子显微学研究

石墨烯（Graphene）是近几年迅速发展起来的研究热点材料之一.利用透射电子显微镜（TEM）研究Graphene的结构特征和原子动态过程,是 Graphene研究的重要进展.文章评述了利用透射电子衍射方法对Graphene的层数、堆垛方式、取向和表面形貌等结构特征进行的研究工作,介绍了利用高分辨透射电子显微术在Graphene的表面缺陷、边缘结构及吸附原子等研究领域取得的最新结果.     

Prospects of anionic nanolipoplexes in nanotherapy: transmission electron microscopy and light scattering studies

Currently nanosystems composed of polynucleotides and lipid vesicles (nanolipoplexes) are considered to be promising tools for gene therapeutics. Successful in vivo application of these vectors depends on their physicochemical, technological and biological characteristics including morphology, size distribution, molecular interactions and stability. Anionic nanoliposomes (DPPC:DCP:CHOL) were prepared by two different techniques, namely the conventional thin-film hydration method followed by extrusion, and the heating method (HM), in which no volatile solvent or detergent is used. A non-viral and non-cationic gene transfer vector was constructed by incorporating plasmid DNA (pcDNA3.1/His B/lacZ) to the HM-nanoliposomes by the electrostatic mediation of Ca²⁺ ions. Transfection efficiency of the nanolipoplexes was evaluated using a human bronchial epithelial cell line (16HBE14o-) in the presence of serum. Particle characterisation, stability of the formulations and lipid–DNA interaction studies were performed using transmission electron microscopy (TEM) and light scattering. TEM pictures of nanolipoplexes showed presence of two to four closely packed vesicles with signs of fusion. Efficient delivery of plasmid DNA and subsequent β-galactosidase expression was achieved using the anionic nanolipoplexes. Transfection efficiency increased with lipid:DNA ratio up to 7:1 (w/w), where transfection efficiency was 12-fold higher than in untreated cells. Further increase in lipid ratio decreased transfection. These nanolipoplexes appear to be safe, stable and efficient in the protection and delivery of DNA to different cells and tissues.     

Phase propagation of localized surface plasmons probed by time-resolved photoemission electron microscopy

In combining time-resolved two-photon photoemission (TR-2PPE) and photoemission electron microscopy (PEEM) the ultra-fast dynamics of collective electron excitations in silver nanoparticles (localized surface plasmons – LSPs) is probed at fs and nm resolution. Here we demonstrate that the sampling of the LSP dynamics by means of time-resolved PEEM enables detailed insight into the propagation processes associated with these excitations. In phase-integrated as well as phase-resolved measurements we observe spatio-temporal modulations in the photoemission yield from a single nanoparticle. These modulations are assigned to local variations in the electric near field as a result of the phase propagation of a plasmonic excitation through the particle. Furthermore, the control of the phase between the fs pump and probe laser pulses used for these experiments can be utilized for an external manipulation of the nanoscale electric near-field distribution at these particles. PACS 78.47.+p; 78.67.Bf; 79.60.-i; 73.20.Mf     

Inelastic electron scattering observation using energy filtered transmission electron microscopy for silicon -- germanium nanostructures imaging

This paper presents a new technique using energy filtered TEM (EFTEM) for inelastic electron scattering contrast imaging of Germanium distribution in Si-SiGe nanostructures. Comparing electron energy loss spectra (EELS) obtained in both SiGe and Si single crystals, we found a spectrum area strongly sensitive to the presence of Ge in the range [50-100 eV]. In this energy loss window, EELS spectrum shows a smooth steeply shaped background strongly depending on Ge concentration. Germanium mapping inside SiGe can thus be performed through imaging of the EELS background slope variation, obtained by processing the ratio of two energy filtered TEM images, respectively, acquired at 90 and 60 eV. This technique gives contrasted images strongly similar to those obtained using STEM Z-contrast, but presenting some advantages: elastic interaction (diffraction) is eliminated, and contrast is insensitive to polycrystalline grains orientation or specimen thickness. Moreover, since the extracted signal is a spectral signature (inelastic energy loss) we demonstrate that it can be used for observation and quantification of Ge concentration depth profile of SiGe buried layers.     

应用动态光散射和透射电镜研究热力学不相容条件下果胶与乳清蛋白混合体系的微观结构

应用动态光散射、透射电镜和粘度-剪切模型3种方法互相配合,研究了果胶与乳清分离蛋白的混合体系在热力学不相容条件下的微观结构。在90℃及pH7.4条件下,向5%蛋白浓度的乳清蛋白溶液中加入带有负电的果胶分子,可导致热变性乳清蛋白分子之间发生损耗聚集,并引发混合体系内的相分离现象。确切地说,当果胶与乳清蛋白的混合重量比小于0.08时,溶液内可观察到粒径小于300nm的聚集颗粒,体系呈现牛顿流体特征;而当混合重量比大于0.08时,体系粘度上升,切稀特征逐渐明显,聚集集团粒径接近700nm。     

Functionalization of gold and silver nanoparticles with diphenyl dichalcogenides probed by surface enhanced Raman scattering

This paper describes a surface‐enhanced Raman scattering (SERS) systematic investigation regarding the functionalization of gold (Au) and silver (Ag) nanoparticles with diphenyl dichalcogenides, i.e. diphenyl disulfide, diphenyl diselenide, and diphenyl ditelluride. Our results showed that, in all cases, functionalization took place with the cleavage of the chalcogen–chalcogen bond on the surface of the metal. According to our density functional theory calculations, the molecules assumed a tilted orientation with respect to the metal surface for both Au and Ag, in which the angle of the phenyl ring relative to the metallic surface decreased as the mass of the chalcogen atom increased. The detected differences in the ordinary Raman and SERS spectra were assigned to the distinct stretching frequencies of the carbon–chalcogen bond and its relative contribution to the ring vibrational modes. In addition, the SERS spectra showed that there was no significant interaction between the phenyl ring and the surface, in agreement with the tilted orientation observed from our density functional theory calculations. The results described herein indicate that diphenyl dichalcogenides can be successfully employed as starting materials for the functionalization of Au nanoparticles with organosulfur, organoselenium, and organotellurium compounds. On the other hand, diphenyl disulfide and diphenyl diselenide could be employed for the functionalization of Ag nanoparticles, while the partial oxidation of the organotellurium unit could be detected on the Ag surface. Copyright © 2011 John Wiley & Sons, Ltd.     

Characterization of LiBC by phase-contrast scanning transmission electron microscopy

LiBC was used as a model compound for probing the applicability of phase-contrast (PC) imaging in an aberration-corrected scanning transmission electron microscope (STEM) to visualize lithium distributions. In the LiBC structure, boron and carbon are arranged to hetero graphite layers between which lithium is incorporated. The crystal structure is reflected in the PC-STEM images recorded perpendicular to the layers. The experimental images and their defocus dependence match with multi-slice simulations calculated utilizing the reciprocity principle. The observation that a part of the Li positions is not occupied is likely an effect of the intense electron beam triggering Li displacement.     

Surface characteristics of Ag‐doped Au nanoparticles probed by Raman scattering spectroscopy

We have examined the surface characteristics of Ag‐doped Au nanoparticles (below 5 mol% of Ag) by means of the surface‐enhanced Raman scattering (SERS) of 2,6‐dimethylphenylisocyanide (2,6‐DMPI) and 4‐nitrobenzenethiol (4‐NBT). When Ag was added to Au to form ∼35‐nm‐sized alloy nanoparticles, the surface plasmon resonance band was blue‐shifted linearly from 523 to 517 nm in proportion to the content of Ag up to 5%. In the SERS spectra of 2,6‐DMPI, the N‐C stretching peak also shifted almost linearly from 2184 to 2174 cm⁻¹ when the Ag content was 5 mol% or less; the peak then remained the same as that of the pure Ag film. The potential variation of the SERS spectrum of 2,6‐DMPI in an electrochemical environment, as well as the effect of organic vapor, also showed a similar tendency. From the SERS of 4‐NBT, we confirmed the occurrence of a surface‐induced photoreaction converting 4‐NBT to 4‐aminobenzenethiol, when Ag was added to Au to form alloy nanoparticles. The photoreaction induction ability also increased linearly with the Ag content, reaching a plateau level at 5 mol% of Ag. All these observations suggest that the surface content of Ag should increase almost linearly as a function of the overall mole fraction of Ag and, once the Au/Ag nanoparticles reach 5 mol% of Ag, their surfaces are fully covered with Ag, showing the same surface characteristics of pure Ag nanoparticles. Copyright © 2011 John Wiley & Sons, Ltd.     

Absorption and scattering of microwaves by falling snow

Fluffy snow flakes are modeled by a polydispersion of hexagonal plates for which analytical expressions for absorption and scattering coefficients are derived using the anomalous diffraction approximation. Comparison with results obtained using the dipole superposition method demonstrates that the accuracy of the anomalous diffraction approximation is within 15%. We also show that replacement of hexagonal plates by equal volume or equal surface area spheres leads to large errors in both scattering and extinction cross sections.     

Structure and mass analysis by scanning transmission electron microscopy.

In the scanning transmission electron microscope (STEM) an electron beam of a few angstroms diameter is raster scanned over a thin sample and the scattered electrons are sequentially measured for each sample element irradiated. The mass, the elemental composition and the structure of a protein can be simultaneously assessed if all detector systems of the STEM are used. Aspects affecting the accuracy of the mass measurement technique and the demands placed on the instrument's dark-field detector system are outlined. In addition, the influences of some sample preparation techniques are noted and the mass-loss induced at ambient temperatures by the incidence of 80kV electrons on various biological samples is reported. Finally, the importance of the STEM for the structural analysis of proteins is documented by examples.     

Polarization features of stimulated electron Raman scattering

An experimental investigation on polarization characteristics of stimulated electron Raman scattering in case of linear and circular polarization of exciting radiation has been undertaken. Theory and experiment are compared. Stark shifts for different components of SERS are determined.